Adrienne V. Li

Structure-based programming of lymph-node targeting in molecular vaccines

In cancer patients, visual identification of sentinel lymph nodes (LNs) is achieved by the injection of dyes that bind avidly to endogenous albumin, targeting these compounds to LNs, where they are efficiently filtered by resident phagocytes. Here we translate this ‘albumin hitchhiking’ approach to molecular vaccines, through the synthesis of amphiphiles (amph-vaccines) comprising an antigen or adjuvant cargo linked to a lipophilic albumin-binding tail by a solubility-promoting polar polymer chain. Administration of structurally optimized CpG-DNA/peptide amph-vaccines in mice resulted in marked increases in LN accumulation and decreased systemic dissemination relative to their parent compounds, leading to 30-fold increases in T-cell priming and enhanced anti-tumour efficacy while greatly reducing systemic toxicity. Amph-vaccines provide a simple, broadly applicable strategy to simultaneously increase the potency and safety of subunit vaccines.

Enhancing humoral responses to a malaria antigen with nanoparticle vaccines that expand Tfh cells and promote germinal center induction.

For subunit vaccines, adjuvants play a key role in shaping immunological memory. Nanoparticle (NP) delivery systems for antigens and/or molecular danger signals are promising adjuvants capable of promoting both cellular and humoral immune responses, but in most cases the mechanisms of action of these materials are poorly understood. Here, we studied the immune response elicited by NPs composed of multilamellar “stapled” lipid vesicles carrying a recombinant Plasmodium vivax circumsporozoite antigen, VMP001, both entrapped in the aqueous core and anchored to the lipid bilayer surfaces. Immunization with these particles and monophosphoryl lipid A (MPLA), a US Food and Drug Administration–approved immunostimulatory agonist for Toll-like receptor-4, promoted high-titer, high-avidity antibody responses against VMP001, lasting more than 1 y in mice at 10-fold lower doses than conventional adjuvants. Compared to soluble VMP001 mixed with MPLA, VMP001-NPs promoted broader humoral responses, targeting multiple epitopes of the protein and a more balanced Th1/Th2 cytokine profile from antigen-specific T cells. To begin to understand the underlying mechanisms, we examined components of the B-cell response and found that NPs promoted robust germinal center (GC) formation at low doses of antigen where no GC induction occurred with soluble protein immunization, and that GCs nucleated near depots of NPs accumulating in the draining lymph nodes over time. In parallel, NP vaccination enhanced the expansion of antigen-specific follicular helper T cells (Tfh), compared to vaccinations with soluble VMP001 or alum. Thus, NP vaccines may be a promising strategy to enhance the durability, breadth, and potency of humoral immunity by enhancing key elements of the B-cell response.

Robust IgG responses to nanograms of antigen using a biomimetic lipid-coated particle vaccine

New subunit vaccine formulations with increased potency are of interest to improve immune responses against poorly immunogenic antigens, to avoid vaccine shortages in pandemic situations, and to promote dose-sparing of potent adjuvant molecules that can cause unacceptable side effects in prophylactic vaccination. Here we report strong class-switched, high avidity humoral immune responses elicited by a vaccine system based on poly(lactide-co-glycolide) micro- or nano-particles enveloped by PEGylated phospholipid bilayers, with protein antigens covalently anchored to the lipid surface and lipophilic adjuvants inserted in the bilayer coating. Strikingly, these particles elicited high endpoint antigen-specific IgG titers (>10(6)) sustained for over 100 days after two immunizations with as little as 2.5 ng of antigen. At such low doses, the conventional adjuvant alum or the molecular adjuvants monophosphoryl lipid A (MPLA) or α-galactosylceramide (αGC) failed to elicit responses. Co-delivery of antigen with MPLA or αGC incorporated into the particle bilayers in a pathogen-mimetic fashion further enhanced antibody titers by ~12-fold. MPLA provided the highest sustained IgG titers at these ultra-low antigen doses, while αGC promoted a rapid rise in serum IgG after one immunization, which may be valuable in emergencies such as disease pandemics. The dose of αGC required to boost the antibody response was also spared by particulate delivery. Lipid-enveloped biodegradable micro- and nano-particles thus provide a potent dose-sparing platform for vaccine delivery.

Generation of Effector Memory T Cell–Based Mucosal and Systemic Immunity with Pulmonary Nanoparticle Vaccination

A lipid nanocapsule vaccine promotes cross-presentation of antigen with enhanced draining lymph node delivery to elicit an effector memory CD8+ T cell response. Nanoparticle Vaccine Delivered to Lungs Delivering vaccines to the lungs has been shown to protect against not only respiratory infections but also pathogens that enter in other organs, including the gastrointestinal and reproductive tracts. To capitalize on this phenomenon, Li and colleagues designed a pulmonary vaccination strategy that uses nanoparticle carriers to deliver antigen and adjuvant to the mucosal surface lining the lungs. Nanosized particles called interbilayer-crosslinked multilamellar vesicles (ICMVs) were engineered to contain antigen along with two Toll-like receptor agonists, which served as adjuvants to stimulate airway epithelial cells and promote dendritic cell uptake and cross-presentation. Mice that received ICMVs containing the model antigen ovalbumin (OVA) showed a greater T cell response than did those that received soluble OVA vaccine, with more OVA-specific T cells in the lungs after 11 weeks. ICMV-based vaccines were next put to the test in therapeutic tumor and prophylactic viral challenge models. As a therapeutic vaccine, all mice that received OVA-ICMVs after an injection of OVA-expressing melanoma cells resisted tumor formation and had prolonged survival. In the challenge model, animals were first given ICMV vaccines loaded with the peptide antigen AL11 [from simian immunodeficiency virus (SIV) gag], then exposed to vaccinia virus expressing SIV gag. Only animals that received pulmonary vaccination—not subcutaneous or soluble vaccine—were protected from viral challenge, showing a reduction of viral titers in the lungs and other organs. The nanoparticle vaccine demonstrated systemic protection when delivered locally to the lung mucosa. The authors suggest that ICMV vaccines stimulated the generation of a large population of effector memory T cells in the lungs and circulation, thus conferring such high protection in mice. Although the ICMVs were determined to be safe and well tolerated in small animals, additional safety and efficacy studies will be needed in larger animals before translation. Many pathogens infiltrate the body and initiate infection via mucosal surfaces. Hence, eliciting cellular immune responses at mucosal portals of entry is of great interest for vaccine development against mucosal pathogens. We describe a pulmonary vaccination strategy combining Toll-like receptor (TLR) agonists with antigen-carrying lipid nanocapsules [interbilayer-crosslinked multilamellar vesicles (ICMVs)], which elicit high-frequency, long-lived, antigen-specific effector memory T cell responses at multiple mucosal sites. Pulmonary immunization using protein- or peptide-loaded ICMVs combined with two TLR agonists, polyinosinic-polycytidylic acid (polyI:C) and monophosphoryl lipid A, was safe and well tolerated in mice, and led to increased antigen transport to draining lymph nodes compared to equivalent subcutaneous vaccination. This response was mediated by the vast number of antigen-presenting cells (APCs) in the lungs. Nanocapsules primed 13-fold more T cells than did equivalent soluble vaccines, elicited increased expression of mucosal homing integrin α4β7+, and generated long-lived T cells in both the lungs and distal (for example, vaginal) mucosa strongly biased toward an effector memory (TEM) phenotype. These TEM responses were highly protective in both therapeutic tumor and prophylactic viral vaccine settings. Together, these data suggest that targeting cross-presentation–promoting particulate vaccines to the APC-rich pulmonary mucosa can promote robust T cell responses for protection of mucosal surfaces.

Vaccine delivery with microneedle skin patches in nonhuman primates

Peter C. DeMuth1,2, Adrienne V. Li1, Peter Abbink3, Jinyan Liu3, Hualin Li3, Kelly A. Stanley3, Kaitlin M. Smith3, Christy L. Lavine3, Michael S. Seaman3, Joshua A. Kramer4, Andrew D. Miller4, Wuhbet Abraham1,2,5, Heikyung Suh1,2,5, Jamal Elkhader1, Paula T. Hammond2,6,7, Dan H. Barouch3,8, and Darrell J. Irvine1,2,7,8,9 1Department of Biological Engineering, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts, 02139 USA